Joining staples for conveyor belts, belts and similar products composed of an upper plate and a lower plate, both said plates being connected at one end by one or several narrower portions called knuckles are known, with said staples being able to be mounted in two series each enclosing one end of the conveyor belt between the upper plates and the lower plates of the staples in each series, the same operation being carried out again on the other end of the conveyor belt while shifting the knuckles of the second series of staples with respect to those of the first series, so that the knuckles of the second series are engaged between the knuckles of the first series. A connecting and articulating rod is then engaged into one knuckle of a series of staples and then into one knuckle of the other series of staples and so on, thus making the equivalent of a hinge.
As regards the attaching of staples at conveyor belt ends which they enclose between upper plate/lower plate couples, various means are used, with two means being the most common ones when considering the development of the related technology.
The most common staple attaching means consists of U-shaped clips made of round metal wire. Such clips include a back composed of a rectilinear round wire portion extended at both ends by pointed branches made of the same wire and bent at right angles with respect to the back. The spikes of the round wire branches are obtained by machining, i.e. milling or grinding.
A second known means for attaching staples is composed of claws extending the upper plate of the staple downwards.
The clips made of U-shaped metal wire are inserted into holes provided in the upper plate of the staples. The pointed branches go through the end of the conveyor belt inserted between the upper plate and the lower plate of the staple. The claws extending the upper plate of a staple are directly inserted into the end of the conveyor belt inserted between the two plates.
Initially, the pointed branches of the clips, when inserted through the thickness of the conveyor belt end, would meet corresponding holes provided in the other plate of the staple, then would go through such holes and be bent onto the outside of the lower plate of the staple. Similarly, the claws inserted along a similar path would also be bent onto the outside of the lower plate. This bend was made using an appropriately shaped matrix positioned under the lower plate. However, this relatively rudimentary means had the disadvantage consisting in that the spikes folded to the outside would make the clip liable to stripping during the operation of the conveyor belt.
To overcome these disadvantages, two prior documents, patent FR 2 792 050 of Apr. 12, 1999 and European patent publication No. 0 464 399 (filing No. 91 109 427.4) have proposed solutions.
Patent FR 2 792 050 has proposed, in the case of staples with claws incorporated in the upper plate, producing doors 5 formed by a bar of the material constituting the lower plate, oriented parallel to the edge of the lower plate situated opposite the hinge elements and raised with respect to the general plane of the lower plate, a shearing being provided on each side of the bar, and raising the edge of the lower plate situated opposite the hinge elements such that it has “a curved profile”, “the claws 4 of the upper plate, the doors 5 and the raised edge 6 of the lower plate being respectively arranged in such a way that when the initially open staple is closed, the spikes of the claws meet the raised edge 6 with a curved profile in the top portion thereof on the side of the raised edge with a curved profile oriented towards the hinge elements of the staple”. This arrangement made it possible to pass the spikes of the claws below the door, locking them at a location situated between the lower face of the conveyor belt and the upper face of the lower portion of the conveyor belt (see FIG. 8 of this patent of the prior art).
Patent EP 0 464 399 also provides (see FIG. 8) a bridge, or door 14 in the lower plate. This bridge is flanked by two holes 13 and 15 provided for the passage of a round wire clip branch. In order to curve the bottom portion of the round wire of the branch of the clip in such a way, when the clips are inserted, as to pass, by means of folding, this bottom portion below the bridge, then into the hole 15 so as to be placed between the lower face of the end of the conveyor belt and the upper face of the lower plate of the staple. An outer matrix of particular shape (see FIG. 7) is, however, indispensable to cause this folding and this routing of the spike of the branch.
The disadvantages presented by the solution of patent FR 2 792 050 consist in the fact that the claws are composed of the same metal as that of the staples, and that therefore it is not possible to choose a metal particularly suited to the clip function, in the fact that the guidance of the spike provided by the raised edge of the lower plate is not perfect, and finally in the fact that the location of the claws is imposed as is the location and orientation of the doors. The disadvantages seriously limit the fields of use of these staples, in particular with regard to heavy conveyor belts which must often be troughed for transporting bulk materials (coal, lignite, ores, phosphates).
The disadvantages presented by the solution of European patent EP 0 464 399 consists in the fact that it uses round wire clips which have only two branches and that it requires the use of an outer matrix of particular shape which must be perfectly positioned to receive the spikes of the clip branches.
The drawback of round wire clips lies in the fact that in order to have an excellent bending strength, it is necessary to increase the diameter thus causing difficulties resulting from the induced over-thickness which cannot be totally accommodated in a recess of the upper plate of the staple, which created problems with the scrapers. In addition, the clips made of round wire include branches, the end portions and spikes of which are made by grinding or milling, have mechanical properties which do not differentiate them from the rest of the clips, i.e. the back of the clips and the body of the branches. For bending the lower portions of the branches, steel wires are generally chosen, the mechanical properties of hardness and bending strength of which are average, with a view to prevent breaking during the bending operations. Such properties are in contradiction with those which are required for the spikes of the branches to go without any difficulty and any deviation through the reinforcing frames of the elastomeric material of the conveyor belts.
It should be noted that, on the clip-staple assembly of patent EP 0 464 399, the staple is provided, in the upper portion thereof, with a recess making it possible to accommodate most of the thickness of the back of the clip. However, a small over-thickness which is liable to be hit by the scrapers remains. If it is desired to increase the diameter of the round wire clip to obtain a better strength therefrom, the problem becomes impossible to solve since it would be necessary to increase the thickness of the upper plate of the staple which can also be hit by the scrapers.
It should be understood that the clips made of round wire cannot be improved because of their basic design.
The means necessary for folding the branches of the clips, in the case of patent EP 0 464 399, involve an outer matrix of a suitable shape for grooving and folding the end portion of the branches, and also a very precise positioning of this matrix, in the most perfect possible alignment with the outlet of the end portion of the branches, outside of the respective holes of the lower plate of the staple.
Now, the conditions of use of conveyor belts, whether in mines, open-air quarries, the transport over long distances of coal, ores, lignite, phosphates, etc., are very severe, and the use of a simple flat anvil, which does not need to be positioned with precision, as is the case with the staples of patent FR 2 792 050, has proved to be very favorable for users. The inventor of the present invention has therefore sought a solution to all these problems, reconciling the contradictory demands imposed by the conditions of installing joining staples, by the conditions of positioning conveyor belts and the necessary strength of the assembly, etc.